Method for producing viscose rayon



United 3,063,789 Patented Nov. 13, 1962 ice 3,063,789 METHOD FQR PRODUCTNG VECQSE RAYON William P. Dooley, Wailingford, Pa., assignor to American Viscose Corporation, Philadelphia, Pa, a corporation of Delaware No Drawing. Filed Nov. 29, 19nd, Ser. No. 72,318 6 Claims. (Cl. 1854) This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated cellulose from viscose.

in the conventional methods of producing shaped bodies of regenerated cellulose from viscose, a suitable cellulosic material such as purified cotton linters, wood pulp, mixtures thereof, and the like is first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the treated cellulose material, it is allowed to age. The aged alkali cellulose is then converted to a xanthate by treatment with carbon disulfide. The cellulose Xanthate is subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and alkali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containing zinc sulfate. The filament may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dilute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to washing, purification, bleaching, possibly other treating operations and drying, being collected either before or after these treatments.

The filaments as formed by the conventional methods, consist of a skin or outer shell portion and a core portion with a sharp line of demarkation between the two. The cross-section of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent metal salts are present in the spinning bath. The skin and core portions of the filament represent differences in structure and these different portions possess different swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resistance and a low flex-life, is subjected to fibrillation and is relatively stiff.

The principal purpose of the present invention is to provide a method for the production of high tenacity regenerated cellulose products and specifically filaments also having an improved resistance to soiland abrasion and an improved fatigue life.

A further purpose of the invention is to provide a viscose spinning solution adapted to form regenerated cellulose products having enhanced physical properties and characteristics.

it has now been discovered that the presence of small amounts of cyclohexanone oxime in viscose results in the production of shaped bodies of regenerated cellulose such as filaments, films, sheets and the like composed of at least about 70% skin and having improved properties and characteristics providin that the amount of the modifying agent is maintained with certain limits and the composition of the spinning bath is maintained within certain composition limits which will be defined hereinafter. The most readily distinguishable characteristics as compared to conventional filaments include a smooth, non-crenulated surface and the filaments have a high tenacity and an improved resistance to soil and abrasion.

The amount of the modifying agent, cyclohexanone oxime, which is incorporated in the viscose must be at least about 2% by weight of the cellulose and may vary up to about 6%, preferably, the amount varies from about 3% to 4%. Lesser amounts do not result in the production of products having the enhanced properties as described hereinbefore and greater amounts affect adversely the physical properties of the products. Amounts within the preferred range are most effective in enhancing the characteristics and properties of the products. The modifying agent may be added at any desired stage in the production of the viscose such as in the preparation of the refined wood pulp for the manufacture of viscose, before or during shredding of the alkali cellulose, to the xan thated cellulose while it is being dissolved in the caustic solution or to the viscose solution before or after filtration. Preferably, the cyclohexanone oxime is added after the cellulose Xanthate has been dissolved in the caustic solution and prior to filtration.

The viscose composition may vary widely as is well known and, for example, it may contain from about 6% to about 10% cellulose, from about 4% to 8% alkali metal hydroxide such as caustic soda and from about 30% to 50%, based on the weight of the cellulose, of carbon disulfiide. The particular source of the cellulose is select-' ed based upon the ultimate use of the regenerated cellulose product. The modified viscose, that is, a viscose containing the small amount of the cyclohexanone ox ime, may have a sodium chloride salt test above about 8 and preferably about 9 or higher at the time of spinning or extrusion.

In order to obtain the improvements enumerated hereinbefore, it is essential that the composition of the spinning bath be maintained within a well defined range. The presence of the cyclohexanone oxime in the viscose combined with these limited spinning baths results in the production of products such as filaments of improved properties such as high tenacity, high abrasion resistance, high fatigue resistance and consisting of filaments composed of at least about 70% skin.

Generically and in terms of the industrial art, the spinning bath is a low acid-high zinc spinning bath. The bath should contain from about 10% to about 25% sodium sulfate and at least about 3% to about 15% zinc sulfate, preferably from 15% to 22% sodium sulfate and from 4% to 9% zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the zinc sulfate. The temperature of the spinning bath may vary from about 25 C. to about C., preferably between about 45 C. to about 70"v C. In the production of filaments, the temperature of, the spinning bath is not critical, however, as is well known in the conventional practice in the art, certain of the physical properties such as tensile strength vary directly with the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is preferably maintained at a temperature between about 55 C. and 70 C. so as to obtain the desired high tensile strength.

The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration Ct at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. For commercial operations, the acid concentration is generally maintained about 0.4% to 0.5% above the slubbing point. For any specific viscose composition, the acid concentration of the spinning bath must be maintained above the slubbing point and below the concentration at which the neutralization of the caustic of the viscose is sufficiently rapid to form a filament having a skin and core.

There is a maximum acid concentration for any specific viscose composition beyond which the improved filaments are not formed. For example, in. general, the acid concentration of the spinning baths which are satisfactory for the commercial production of the improved regenerated cellulose products from a 7% cellulose, 6% caustic viscose, lies between about and about 8%. The acid concentration may be increased as the amount of modifier and carbon disulfide is increased and also as the salt test of the viscose is increased. There is an upper limit, however, for the acid concentration based upon the amount of modifier and the concentration of caustic in the viscose. The thick skinned products of this invention cannot be obtained if the acid content of the bath is increased above the maximum value although the amount of added modifier is increased beyond about 5% while other conditions are maintained constant. Increasing the caustic content of the viscose beyond about 8% is uneconomical forcommercial production methods. For example, a viscose containing about 7% cellulose, about 6% caustic soda, about 36%, based on the weight of the cellulose of carbon disulfide and 2%, based on the weight of the cellulose, of cyclohexanone oxime and having a salt test or" 9 to 10 Whenextruded into spinning baths containing 16% to 20% sodium sulfate, 4% to 8% zinc sulfate and sulfuric acid not more than about 8%, results in the production of filaments having the enhanced properties. Lesser amounts of sulfuric acid may be employed. Greater amounts of acid result in the production of products having lesser proportions of skin and lower physical properties. It has been determined that the maximum permissible acid content of the bath is about 10%. A lowering of the amount of modifier, the lowering of the caustic soda content or the lowering of the salt test of the viscose reduces the maximum permissible acid concentration for the production of filaments having the aforementioned properties.

The presence of cyclohexanone oxime in the viscose retards the coagulation and, therefore, the amount of modifier employed must be reduced at high spinning speeds. Thus, for optimum physical characteristics of filaments formed from a viscose as above and at a spinning speed of about 50 meters per minute, the adduct is employed in amounts within the lower portion of the range, for example, about 2% to 3%. The determination of the specific maximum and optimum concentration of acid for any specific viscose, spinning bath and spinning speed is a matter of simple experimentation for those skilled in the art. The extruded viscose must, of course, be immersed or maintained in the spinning bath for a period sufiicient to effect relatively complete coagulation of the viscose, that is, the coagulation must be sufiicient so that the filaments will not adhere to each other as they are brought together and withdrawn from the bath.

In the production of filaments for such purposes as the fabrication of tire cord, the filaments are preferably stretched after removal from the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot water or a dilute acid solution and may be stretched from about 70% to about 110%, pref erably between 75% and 100%. Filaments for other textile purposes may be stretched as low as 20%. The precise amount of stretching will be dependent upon the desired tenacity and other properties and the specific type of product being produced. If desired, the filaments may be stretched in air. It is to be understood that the invention is not restricted to the production of filaments and yarns but it is also applicable to other shaped bodies such as sheets, films, tubes and the like. The filaments may then be passed through a final regenerating bath which may contain from about 1% to about 5% sulfuric acid and from about 1% to about 5% sodium sulfate with or without small amounts of zinc sulfate if regeneration has not previously been completed.

The treatment following the final regenerating bath, or the strctchin operation where regeneration has been completed, may consist of a washing step, a desulfurizing step, the application of a finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the proposed use thereof.

Regenerated cellulose filaments prepared from viscose containing the small amounts of cyclohexanone oxime and spun in the spinning baths of limited acid content have a smooth or non-crenulated surface and consist of at least about 70% skin. Filaments produced pursuant to this invention and consisting of at least about 70% skin have a high toughness and a greater flexing life which may be attributed to the diffuse boundary between the skin and core. Although the twisting of conventional filaments, as in the production of tire cord, results in an appreciable loss of tensile strength, there is appreciably less loss in tensile strength in the production of twisted cords from the filaments formed in accordance with this invention. Filaments prepared from viscose containing cyclohexanone oxime have a high tensile strength in both the wet and dry state as compared to normal regenerated cellulose filaments and to filaments formed from viscose containing prior modifiers, have superior abrasion and fatigue resistance characteristics and have a high flexlife. Such filaments are highly satisfactory for the production of cords for the reinforcement of rubber products such as pneumatic tire casings, but the filaments are not restricted to such uses and may be used for other textile applications.

The invention may be illustrated by reference to the preparation of regenerated cellulose filaments from a viscose containing 6.25% cellulose, 5.75% caustic soda, and having a total carbon disulfide content of about 39% based on the weight of the cellulose. The viscose solutions were prepared by xanthating alkali cellulose by the introduction of 39% carbon disulfide, based on the weight of the cellulose, and churning for about 2 /2 hours. The cellulose xanthate was then dissolved in caustic soda solution. The cyclohexanone oxime was added to the caustic soda solution and mixed for about /2 hour. The viscose was then allowed to ripen for about 28 hours at 18 C.

The modified viscose was extruded to form a yarn of 600 denier, 400 filaments at a spinning speed of approximately 50 meters per minute. The coagulating and regenerating bath contained about 7.5% sulfuric acid, 6.35% zinc sulfate and about 15% sodium sulfate and was maintained at a temperature of about 65 C. The yarn after removal from the spinning bath was passed through an aqueous bath maintained at about C. and was stretched 95% while passing through the hot aqueous liquid. The yarn was then collected in a spinning box, washed free of acids and salts and dried. In one example, the hot aqueous bath consisted of water, while in a second example, the hot aqueous bath consisted of a 3% sulfuric acid solution.

In a like manner, filaments were formed from viscose having the same cellulose, caustic soda and carbon disulfide content utilizing prior modifying agents, namely, cyclohexylamine (US. Patent No. 2,535,044) and an ethylene oxide adduct of ethylene diamine containing an average of about 50 ethylene oxide units per mole of ethylene diamine (US. application Serial No. 807,298, filed April 20, 1959, and now Patent No. 2,984,541). Viscose modified by the addition of these agents was spun under the same conditions as described for the spinning of the cyclohexanone oxime modified viscose. The physical properties of the filaments are as follows:

oxime; OHAcyclohexylarnine; DED- 1 CEO-cyclohexanone ethylene oxide-ethylene dramrne adduct.

The filaments have a smooth, non-crenulated exterior surface and exhibit a diffuse boundary between skin and core at high magnification (e.g. 1500 Filaments formed from the same Viscose and spun under substantially identical conditions but without the added modifier exhibit a very irregular and serrated surface with a sharp line of demarkation between the skin and core.

Although the tenacity and elongation are the only properties set forth, they have been chosen because of the ease and simplicity with which such properties may be determined. It will be noted that products made in accordance with this invention exhibit improvements in tensile strength and elongation as compared to products formed of viscose containing prior modifiers. The products also possess improved abrasion resistance, flex-life and other properties disclosed hereinbefore.

One of the properties of conventional textile grades of viscose rayon which has limited its uses is its relatively high cross-sectional swelling when wet with water, this swelling amounting to from about 65% to about 80% for rayon produced by conventional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45% to about 60%.

The cyclohexanone oxime may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrative purposes. The modifying agent may be added at any desired stage in the production of the viscose and may be present in the cellulosic raw material although it may be necessary to adjust the amount present to produce a viscose having the proper proportion of the modifying agent at the time of spinning.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A

(General Dyestuffs Corp.) for 1 to 2 hours.

microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyers albumin fixative. After dewaxing in xylene, the section is placed in successive baths of and 30% alcohol for a few moments each, and it is then stained in 2% aqueous solution of Victoria Blue BS cone. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10% water and dioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and it is to be understood that changes and variations may be made Without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. In a method of producing shaped bodies of regenerated cellulose, the steps which include extruding viscose containing from about 2% to about 6%, based on the weight of the cellulose, of cyclohexanone oxime into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate and not more than about 10% sulfuric acid.

2. In a method as defined in claim 1 wherein the proportion of cyclohexanone oxime is between 3% and 4%, based on the weight of the cellulose in the viscose.

3. The method of producing shaped bodies of regenerated cellulose which comprises adding to and incorporating in viscose from about 2% to about 6%, based on the weight of the cellulose, of cyclohexanone oxime, the viscose containing from about 6% to 10% cellulose, from about 4% to 8% caustic soda and from about 30% to 50% carbon disulfide, based upon the weight of the cellulose, and extruding the Viscose into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate and not more than about 10% sulfuric acid.

4. The method as defined in claim 3 wherein the proportion of cyclohexanone oxime is between 3% and 4%, based on the weight of the cellulose in the viscose.

5. A viscose spinning solution containing from about 2% to about 6%, based on the weight of the cellulose in the viscose of cyclohexanone oxime.

6. A viscose spinning solution as defined in claim 5 wherein the proportion of cyclohexanone oxime is between 3% and 4%, based upon the weight of the cellulose in the viscose.

Hollihan Sept. 16, 1958 Thumm Sept. 23, 1958 

1. IN A METHOD OF PRODUCING SHAPED BODIES OF REGENERATED CELLULOSE, THE STEPS WHICH INCLUDE EXTRUDING VISCOSE CONTAINING FROM ABOUT 2% TO ABOUT 6%, BASED ON THE WEIGHT OF THE CELLULOSE, OF CYCLOHEXANONE OXIME INTO AN AQUEOUS SPINNING BATH CONTAINING FROM ABOUT 10% TO 25% SODIUM SULFATE, FROM ABOUT 3% TO 15% ZINC SULFATE AND NOT MORE THAN ABOUT 10% SULFURIC ACID. 